The present invention relates to a safety belt restraining system for vehicles, comprising a belt retractor with a frame and a webbing clamping means arranged downstream of the retractor and having two clamping wedges which are arranged opposite each other in a housing on either side of the webbing.
In such a system, which for example is known from DE-OS-3,330,938, the webbing clamping means serve the purpose of eliminating or at least reducing the film reel effect on blocking of the belt retractor activated in vehicle-sensitive or webbing-sensitive manner, said effect being the cause for the withdrawal of a few centimeters of webbing length by tightening of the webbing coil after blocking of the webbing reel in conventional belt retractors. Furthermore, the webbing clamping means relieves the belt retractor so that the latter can be dimensioned for small mechanical loads.
Webbing clamping means must be able to take up a very large force exerted on the webbing over their relatively small longitudinal extent in the direction of the webbing path. Consequently, in the event of a vehicle collision the webbing is subjected to extremely high loads in the region of the engagement of the clamping means. However, in normal vehicle operation as well, the webbing can be subjected to loads by the webbing clamping means. For it is desirable to keep the response threshold of the webbing clamping means as low as possible to ensure that said clamping means functions as early as possible in the event of a vehicle collision. However, with a low response threshold even in normal vehicle operation the webbing is frequently, usually at the same point, acted upon by the webbing clamping means and in the course of time can be damaged in a manner affecting safety.
The known construction of the webbing clamping means with clamping wedges arranged on either side of the webbing is able to reduce said stresses because the clamping wedges thereof move synchronously to each other so that no relative movement stressing the webbing takes place between them and the webbing is loaded symmetrically on both sides. However, in practical use the webbing nevertheless tears at stresses which lie substantially below the static tearing resistance of the webbing.